integrator_p2_4d_3ang.hh

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#pragma once
 
// DiFfRG
#include <DiFfRG/common/math.hh>
#include <DiFfRG/physics/integration/quadrature_integrator.hh>
 
// standard libraries
#include <array>
 
namespace DiFfRG
{
  namespace internal
  {
    template <typename NT, typename KERNEL> class Transform_p2_4D_3ang
    {
    public:
      using ctype = typename get_type::ctype<NT>;
 
      static constexpr ctype int_prefactor = powr<-4>((ctype)2 * M_PI); // fourier factor
 
      template <typename... T>
      static KOKKOS_FORCEINLINE_FUNCTION NT kernel(const ctype q, const ctype cos1, const ctype cos2, const ctype phi,
                                                   const T &...t)
        requires provides_kernel<NT, KERNEL, ctype, 4, T...>
      {
        using namespace DiFfRG::compute;
 
        const ctype int_element = powr<4 - 1>(q); // from p integral
 
        // sqrt(1. - powr<2>(cos1)); // the cos1 integral jacobian is already included
        // in the chebyshev2 quadrature
 
        const NT result = KERNEL::kernel(q, cos1, cos2, phi, t...);
 
        return int_prefactor * int_element * result;
      }
 
      template <typename... T>
      static KOKKOS_FORCEINLINE_FUNCTION NT constant(const T &...t)
        requires provides_constant<NT, KERNEL, T...>
      {
        return KERNEL::constant(t...);
      }
    };
 
  } // namespace internal
 
  template <int dim, typename NT, typename KERNEL, typename ExecutionSpace>
    requires(dim == 4)
  class Integrator_p2_4D_3ang
      : public QuadratureIntegrator<4, NT, internal::Transform_p2_4D_3ang<NT, KERNEL>, ExecutionSpace>
  {
    using Base = QuadratureIntegrator<4, NT, internal::Transform_p2_4D_3ang<NT, KERNEL>, ExecutionSpace>;
 
  public:
    using ctype = typename get_type::ctype<NT>;
    using execution_space = ExecutionSpace;
 
    Integrator_p2_4D_3ang(QuadratureProvider &quadrature_provider, const JSONValue &json)
      requires provides_regulator<KERNEL>
        : Integrator_p2_4D_3ang(quadrature_provider,
                                internal::make_int_grid<4, NT>(json, {"x_order", "cos1_order", "cos2_order", "phi_order"}),
                                optimize_x_extent<typename KERNEL::Regulator>(json))
    {
    }
 
    Integrator_p2_4D_3ang(QuadratureProvider &quadrature_provider, const std::array<size_t, 4> grid_size,
                          ctype x_extent = 2.)
        // The azimuthal angle phi in [0,2pi) has a smooth 2pi-periodic integrand; the periodic trapezoidal
        // rule integrates it with spectral (exponential) accuracy, unlike Gauss-Legendre.
        : Base(quadrature_provider, grid_size, {0, 0, -1, 0}, {std::sqrt(x_extent), 1, 1, 2 * M_PI},
               {QuadratureType::legendre, QuadratureType::chebyshev2, QuadratureType::legendre,
                QuadratureType::trapezoidal}),
          x_extent(x_extent), k(1.)
    {
    }
 
    void set_x_extent(ctype x_extent)
    {
      this->x_extent = x_extent;
      Base::set_grid_extents({0, 0, -1, 0}, {std::sqrt(x_extent) * k, 1, 1, 2 * M_PI});
    }
 
    void set_k(ctype k)
    {
      this->k = k;
      Base::set_grid_extents({0, 0, -1, 0}, {std::sqrt(x_extent) * k, 1, 1, 2 * M_PI});
    }
 
  private:
    ctype x_extent;
    ctype k;
  };
} // namespace DiFfRG